Please allow me to write my first post and to share my small experience:

In order to match a 7D and a Canon 70-200 f4 IS, I purchased following extenders in June 2012:- Kenko Teleplus MC PRO 300 DGX 2.0x, then...- Canon Canon Extender EF 2x III

The reason I sent the Kenko back doesn't show on samples:I found I was unable to achieve reliable focus:I made small tests on contrasty building fronts, 200m distance, center point AF, under cloudy skies.In 50% of the cases, focus was achieved after 4 seconds.In 25% of the cases, the 7D reported no focus.

I found it not acceptable for my use.I never faced such issues with the Canon 1.4x II, I owned before.I am aware that handling f4 and 2x might be beyond the 7D's capacity.

Sadly, sharpness and color with the Kenko seemed ok to me.(I do have samples using the Kenko, but I now know that I didn't spend enough time AFMA'ing my 70-200)

I now use the Canon 2x III on a Canon 70-200 f2.8 IS II, and I am very pleased with the match.The Canon 2x III doesn't show the ugly OOF-artifacts I observed on the 1.4x II.

I hope this is useful to some extent,Looking forward to having feedback from other users.

You should only consider extenders if cropping won't do it. The extender basically is an magnifying glass making the image bigger but doesn't add sharpness if the lens doesn't already have much more sharpness than the sensor.

Regarding sharpness there are very mixed reports. It seems to depend on the lens-extender combination how well it works. If you are unlucky and the manufacturing errors of both devices add up you'll get poor quality even though both alone seem ok. Canon extenders are designed to work well with the long lenses (300 and up). That's also the reason why they are so expensive. If you spend 10k on a lens 1k for the extenders won't hurt.

Focusing is slower but works well for me (canon 2x-III) with very good light. Also stopping down one stop is needed to achieve acceptable image quality (F2.8 original lens * 2 extender * 1.4 = F8).

I now use the Canon 2x III on a Canon 70-200 f2.8 IS II, and I am very pleased with the match.The Canon 2x III doesn't show the ugly OOF-artifacts I observed on the 1.4x II.Cheers

I am glad that combination has worked for you. I'll share a different experience.

I tried the 7D / 70-200 f2.8 IS II / 2X III combination. Intitial shots showed severe Front Focus Issues. I talked to the folks at CPS about the setup asking if Microadjustment settings would remember the combination as its own lens, or would it also apply those microadjustments to the 70-200 by its self also. They could not answer that question, so I exchanged that extender for another. I later discovered that the combination is remembered as it's own lens.

Based on the intial bad results with the replacement extender (and really wanting that combination to work for me) I tackled lens Microadjustment. What I discovered was that at 400mm, the setup was fairly accurate, (although also somewhat inconsistant) with little or no adjustement needed, but at 200mm I needed to adjust focusing to +12 on the -20 to +20 scale. I decided this was not going to work for me, so I returned the second extender.

I understand that lenses and extenders are built to tolerance ranges, and if the tolerances of the lens and extender are at the oposite ends of that range, problems could result. CPS suggested I borrow one of their 2x's to compare, as the ones I purchased may have be built together with similar tolernces towards one end of the scale. I have not tried that yet. I may give the 1.4x a shot but I really wanted to get to 400mm.

I am aware that handling f4 and 2x might be beyond the 7D's capacity. I now use the Canon 2x III on a Canon 70-200 f2.8 IS II, and I am very pleased with the match.Cheers

Focusing at f8 (f4+2x) is unreliable on the 7D this is a 7D issue and has nothing to do with the kenko converter, except that the kenko allows the camera to try and focus. Put a Canon 2x converter in the same position and the 7D won't even try to focus. The 7D is limited to focusing reliably at f5.6, which is why the f2.8 + 2x works fine.

Thanks Heptagon, those comparisons sure put me off the 2.0x ii & kenko 300 The resulting images are unacceptably blur!. Perhaps the reviewer was a little "unlucky" as you say, with the tolerances because those images seem completely unusable. Are you fellas yielding similar results in RL? Is the image degradation that severe?!

TheFlorist, good to hear that the 2x iii works on the 70-200, that's a lens I'm hoping to add one day so I'll keep that in mind. But Rockets95 review is starting to put me off the 2x all together.

I guess my question now is, are the 1.4's much better than the 2.0's for sharpness retention? And do you guys, owning the canon 2x iii find your images to take a big hit in your images compared to the 1.4x.?

I'm thinking that maybe 1.4x is the way to go, at least start there anyway.

I thought I'd share an image I took yesterday. This is the reason for why I'm looking into magnification, as this is as close as I could get to the little fella with the 100 macro. Would have loved to get more detail!This was shot handheld so the focus plane is a little off, but oh well Cheers

I thought I'd share an image I took yesterday. This is the reason for why I'm looking into magnification, as this is as close as I could get to the little fella with the 100 macro. Would have loved to get more detail!This was shot handheld so the focus plane is a little off, but oh well Cheers

I notice you have a 5D MK III. Be aware that neither the Canon or the Kenko TC's will work with the 100L. The Canon TC's will interfere and will not mount, while the Kenko 1.4X PRO 300 DGX will lockup and require the camera battery to be removed and re-inserted before the TC will function again with the 5D3 and a different lens. You can get a fully manual TC and use manual exposure with the L, but not autofocus.

I thought I'd share an image I took yesterday. This is the reason for why I'm looking into magnification, as this is as close as I could get to the little fella with the 100 macro. Would have loved to get more detail!This was shot handheld so the focus plane is a little off, but oh well Cheers

I thought I'd share an image I took yesterday. This is the reason for why I'm looking into magnification, as this is as close as I could get to the little fella with the 100 macro. Would have loved to get more detail!This was shot handheld so the focus plane is a little off, but oh well Cheers

I notice you have a 5D MK III. Be aware that neither the Canon or the Kenko TC's will work with the 100L. The Canon TC's will interfere and will not mount, while the Kenko 1.4X PRO 300 DGX will lockup and require the camera battery to be removed and re-inserted before the TC will function again with the 5D3 and a different lens. You can get a fully manual TC and use manual exposure with the L, but not autofocus.

I hope there is a update to the TC.

The 5D III gets locked up with the PRO 300 and the 300 mm II lenses as well.

Yes, in macro work is extenders can be useful. One thing I found handy about using an extender is that your subject is bigger in camera. Especially with TS-E lenses where it is hard to focus manually.

Most opinions I heard about the 1.4x were positive. Using the 2x-Extender under good conditions really allows to extract more detail from the subject that it would have been possible without extender. This is especially true when using current FF-cameras. Look at the second image here where the flower is a) cropped-magnified and b) photographed with an 1.4x/2x extender:http://www.the-digital-picture.com/Reviews/Canon-Extender-EF-1.4x-III-Review.aspx

One downside by using an extender I found is that the whole image quality degrades i.e. lower contrast, CA, distortion etc. You have to use postprocessing to achieve the quality of the naked lens.

You should also consider using a crop camera. Especially the predicted 7D-II with 24MP already provides a much higher resolution (in pixels per mm) than the full-frame-cameras. That is like a 18MP full-Frame with a 2x-Extender built in.

I have the Kenko 1.4x 300 DGX version and have not experienced the issues of lockup - this is news to me other than a few comments here by other members.

I will try to do some tests to see if this does happen on my kit - Kenko do state that when mounting/dismounting this TC that the body is powered off due to the electronics inside the TC so this is what I have always followed.

I have tried in very quick succession using the Kenko 1.4x 300 DGX TC with the following Canon lenses on a 5D3 body (FW 1.1.3) 17-40 f4, 35 f1.4, 135 f2, 24-105 IS f4, TS-E 90 f2.8, 100 f2.8 IS L macro, 200 f2.8 II and all appear to function correctly reporting the correct f-stop adjustment and focus as expected.

As mentioned earlier in changing between lenses I ensure that the body is powered off, battery is still installed....this simply could be enough, but I do not use it extensively its a just incase where a bit extra reach is needed. As it has been working I did not go hunting for any compatibility issues.

I have had this DGX model since Jul '11 so not sure if there are newer versions with other FW which could a cause ..